Field of the Invention
A technique disclosed in the specification relates to ion implanters, and relates to, for instance, ion implanters that implant ions into semiconductor substrates.
Description of the Background Art
An ion implanter includes an ion source system, a mass spectrometer system, a beam line system, and an end station.
The ion source system ionizes a to-be-implanted element and further applies a high voltage to the ionized element to be thus extracted as ion beams. The mass spectrometer system applies a magnetic field to the ion beams, which are extracted in the ion source system using an electromagnet, thus deflecting travelling directions of the ion beams. The beam line system transports the ion beams.
The end station sets a semiconductor substrate that is a target substrate, and performs an ion implantation process. The end station is provided with an electron shower generator that supplies secondary electrons.
Desired ions of the element that have passed through the beam line system are radiated to the semiconductor substrate, which is set in the end station. Being irradiated with the ions of the element that have electric charges, the semiconductor substrate has accumulated electric charges. The semiconductor substrate is thus electrified.
To address this, the secondary electrons from the electron shower generator, which is disposed in the end station, are supplied to the ion beams. Hence, the semiconductor substrate is simultaneously irradiated with both the secondary electrons and the ion beams. Doing so neutralizes the accumulated electric charges within the semiconductor substrate. This prevents the semiconductor substrate from being electrified (for instance, see Japanese Patent Application Laid-Open No. 62-126538).
The passage of time deteriorates a filament that is a generation source of the secondary electrons in an electron shower generator of a conventional ion implanter, where the electron shower generator is used for preventing a semiconductor substrate from being electrified. Consequently, this deterioration changes the amount of secondary electrons supplied from the filament. It has been thus difficult to regulate the secondary electrons to be supplied.
It has been difficult to regulate the secondary electrons to be supplied from the electron shower generator in accordance with implantation energies of the ion beams or with the capacitance of electric charges in the semiconductor substrate as set. In particular, a relatively-large beam current ranging from several tens of milliamperes to several hundreds of milliamperes can polarize the ion beams due to the electric charges of themselves, thus resulting in a non-uniform amount of ions to be implanted. Consequently, it has been difficult to regulate the secondary electrons to be supplied from the electron shower generator.
The relatively-large beam current ranging from several tens of milliamperes to several hundreds of milliamperes may cause the electric charges of the electrified semiconductor substrate to be saturated. In such a case, the semiconductor substrate might have had an abnormal electric discharge in a front surface of the semiconductor substrate, thus damaging a semiconductor element or the semiconductor substrate itself.
On the other hand, a small beam current to prevent the semiconductor substrate from being electrified takes a long time for irradiation due to a decrease in implantation energy. Because of this long time irradiation, the ion implanter has a lower processing capability. Further, if the semiconductor substrate is extremely thin in a relatively-small beam current ranging from several milliamperes to several tens of milliamperes, the abnormal electric discharge might also have damaged the semiconductor element or the semiconductor substrate itself like in the relatively-large beam current.